In the field of document scanners, it is desirable to be able to scan a document with the highest resolution possible and as fast as possible. Furthermore, when there are multiple pages of documents, it is highly desirable to scan the multiple pages automatically with an automatic paper feeder without manual intervention during the process.
Currently, commercial multifunctional scanner-copier-printer-fax machines typically employ a linear scan head as the primary imaging device before one or multiple copies of the scanned image is printed out as a photo copy, or faxed to a receiving fax machine. In this type of multifunctional machine, document is either placed on a platen scan surface while the scan head moves from one edge of the surface to the other to process scanning of the paper one line at a time until the entire surface is scanned, or when an automatic document feeder is present, a document is rolled pass a stationary scan head which is positioned on the paper path to finish scanning one line at a time with the movement of the paper until the entire surface of the document is scanned.
The main drawback of such a prior art scanning mechanism is that it consumes significant time to finish scanning in a linear fashion. For monochrome color scanning, with scanning resolution of approximately 200 dpi, the current scanning mechanism can take multiple seconds, depending on the paper size and whether the device is consumer grade or professional grade.
For higher resolution scanning such as 300 dpi or 600 dpi scanning, the time to finish a full page scanning can be in tens of seconds. For 32-bit or higher color depth full color scanning, the time to finish a single page scanning can take more than 30 seconds, and depending on whether it is a consumer grade scanner, the time required can go beyond 1 minute for a single page.
Also currently available are some document camera products that are designed and used primarily for the purpose of projecting 3D objects on a larger screen for classroom instructions and product or procedure demonstrations. Traditionally, these document cameras are limited by fairly narrow field of view and shallow depth of field due to the primary application requirement of being able to zoom in on objects with greatly magnified views. The images produced by such document camera devices are often only able to show a portion of a full page document clearly, and requires the document to be held fairly flat in order to capture an image that is not blurred.
Such document cameras are not very suitable for capturing images for documents, and are more suitable for 3D, even though they are called document cameras. Additionally, the traditional application of document cameras normally requires projecting real time video onto large screens. The desire for smoothness of the video projection demands limited per frame image resolution so that the cost of video compression and time of video signal transmission is kept low. Such considerations limit the video image quality for document cameras to less than 100 dpi, which is not high enough for scanning documents with printed small font sized letters and other symbols, requiring at least 200 dpi resolution to be reproduced clearly.
As digital cameras began to be integrated into cell phones, laptop PCs, and other personal computers, optical components and digital sensing component, which have become more and more capable in terms of high resolution, color reproduction, and being highly compact, are becoming more and more common place. The cost for such high quality digital imaging components is also reduced significantly which makes it possible to integrate digital camera devices into more and more electronic products. Revising the imaging components in facing-down document cameras, with resolutions as high as 8, 12, 20, or even 30 mega pixels, for the purpose of document imaging or “scanning” at 300 dpi, 600 dpi, or higher, is not only technically feasible, but also increasingly more cost effective.
Scanners or copier technologies are typically used with an automatic document feeder. Such prior art devices typically have a base frame with a platen glass on top, with originals positioned facing down and above a scanning mechanism. A motor typically drives a scan head beneath the original to capture light reflected off individual linear areas of the original. This is the flatbed scanning module of modern day scanners and copiers. It is common place now for scanners and copiers to have an accompanying automatic document feeder module on top of the flatbed scanning base module. When users feed Multiple pages of paper through the document feeder, an elaborate assembly of mechanical and electrical parts are employed to load paper one sheet at a time, and steadily transport each sheet of paper through a scanning mechanism, which emits a beam of light and captures the reflected light through the beam opening, as the paper rolls through, from the feeder, all the way to the output receiving tray. An example of such prior art can be seen in FIGS. 1 and 2, showing a HP® ScanJet 5590 Digital Flatbed Scanner. Such prior art digital imaging devices encounters certain limitations. In one aspect, such prior art devices are limited in speed of scanning.
Commercially available scanners often publish scan time per line between 0.5 ms to several milliseconds depending on the dpi setting. The time delay to finish scanning a full page document is likely caused by not only the mechanical movement of scan head from line to line, but also the processing time required to compose single line images together into a full page image. This per line scan time coupled with the limitation in paper transport speed through often highly complex and elaborate gear and roller assemblies, in order to ensure paper moves through evenly and steadily while in the meantime avoiding any potential paper clogging inside the assemblies, limits the overall speed greatly. As a result, the vast majority of commercially available scanners are limited to scan no more than 30 pages of monochrome colored paper per minute at 300 dpi resolution. For scanning 32-bit or 48-bit colored paper, the speed drops down significantly, sometimes down to single digit number of pages per minute. When the dpi resolution increases, the scan speed also drops down significantly, sometimes even to the level of less than one page a minute for 600 dpi resolution in consumer grade scanners. High speed professional grade scanners do exist at much higher price than a regular consumer can afford. However, even the professional grade scanners suffer significant speed loss when dpi resolution increases and when scanning with color. In another aspect, such prior art digital imaging devices must employ highly elaborate and complex mechanisms to ensure that paper originals can be loaded properly into the scanning mechanism housing, pulled through the scanning mechanism evenly and steadily so that the captured image is of high quality, and to ensure that paper originals are unloaded properly into a receiving tray when scanning is finished.
Such complex mechanical assemblies are most often not space efficient in either surface dimensions or vertical dimension. Furthermore, the higher the scanning speed requirement, the more complex the mechanism is required to be, and the bulkier such devices tend to become. Also, such prior art imaging devices are not suitable for capturing images of 3D objects not in the form of a sheet of paper, due to the flat glass top and the paper loading mechanism.
When there is the need of scanning multiple paged documents, automatic paper feeding methods or systems are no longer suitable for working with these new document camera-scanner devices. An example of a prior art paper loading apparatus is described in U.S. Pat. No. 5,213,426. If one is to follow the general process of paper loading, transporting, scanning, and then unloading, an automatic paper feeder mechanism has to include a highly sophisticated mechanism to stop a sheet of paper completely while ensuring that it is exposed in full view of the camera-scanner looking down, before a complete image can be captured, and before the paper is removed in an unloading action sequence. Following such traditional design, the resulting mechanical assembly required to work with a document camera-scanner, could be even more complex, elaborate, and bulkier than the automatic paper feeder units included in the prior art devices.